Blender 2.9 does not recognize my GPU
Nvidia discontinued the development of the CUDA Toolkit for macOS. The last version that was release for it was 10.2. Consequentially, Blender 2.9x does not include support for CUDA rendering on macOS. This change is documented in the release notes and the manual.

NVIDIA GPU rendering on macOS is no longer supported. Apple dropped support for CUDA drivers in macOS 10.14, and no recent Apple hardware uses NVIDIA graphics cards.


GPU rendering is only supported on Windows and Linux; macOS is currently not supported.

Since Apple has also deprecated their OpenCL compiler it is currently not possible to use GPU rendering with Cycles in Blender 2.9x, until it is ported to Apple's Metal API.
Since Blender 2.83 is an LTS release, I would suggest you continue to use this version.